1. Field of the Invention
The present invention relates generally to fans, and more particularly to a centrifugal fan which has low noise and can generate a high air pressure and a large mount of airflow during operation.
2. Description of Related Art
With the fast development of the electronics industry, electronic components such as CPUs (central processing units), or VGA (video graphics array) are being made with ever faster operating speeds. During operation of the electronic components, a large amount of heat is generated. Greater emphasis is now being laid on increasing the efficiency and effectiveness of heat dissipation devices so as to keep operational temperature of the electronic components within a suitable range, and a centrifugal fan is generally used to provide a forced airflow to increase heat dissipation.
The centrifugal fan typically includes a housing, a hub and a plurality of blades extending radially from the hub and received in the housing. A first air inlet and a second air inlet are defined in central portions of top and bottom surfaces of the housing respectively, and an air outlet is defined in a side wall of the housing and is oriented perpendicularly to the air inlets.
The diameters of the first and second air inlets are equal to each other and are both smaller than the diameter of the fan blades. For avoiding interference between the fan blades and the housing, a clearance must be defined between each of the top and bottom surfaces of the housing and the fan blades. In use, the fan blades rotate to engender an airflow, and the airflow is intaked from the air inlets and is guided into an interior of the centrifugal fan to form a high pressure airflow, which is then discharged towards the electronic component via the air outlet, thus cooling the electronic component continuously. However, the high pressure airflow in the centrifugal fan also impinges on the side wall of the fan and is rebounded back, tending to flow back into the air inlets via the clearances defined between the housing and the blades, which conflicts with the requirement of the fan blades to fully make use of the airflow, thus impairing performance of the centrifugal fan. Additionally, when the airflow intaked from the air inlets mixes with the rebounded airflow, a vortex is formed around the air inlets, which not only reduces the mount of airflow flowing into the housing of the fan but also increases the noise.
For the foregoing reasons, therefore, it is desired to devise a centrifugal fan which can overcome the above-mentioned problems.